Advances in the technology of numerically controlled machine tools have been so great that these numerically controlled machine tools can machine workpieces of complex shape at high speed with precision. At present, workpieces of complex shape cannot be machined without numerically controlled machine tools.
To generate machining programs, there are widely used interactive numerical control apparatuses which comprise a numerical control apparatus with an interactive program generating function, and an automatic programming apparatus for simply generating complex machining programs.
In the use of such a numerical a control apparatus, it is necessary to accurately define machine coordinates, a machine origin, program coordinates, a machining origin, and other data for generating strict machining programs. The interactive numerical control apparatus and the automatic programming apparatus can be used to machine a number of workpieces. However, a portion of a machining process for producing a prototype or a model is carried out solely at the discretion of the operator since no definite workpiece shapes are defined. Therefore, general-purpose milling machines, lathes, or the like are used to machine prototypes or models.
Problems of general-purpose machine tools are that the number of available operators who can handle general-purpose machine tools is becoming smaller, and it is difficult for the general-purpose machine tools to carry out oblique linear machining, arcuate machining, or the like though they can effect linear machining without any problem.
If, on the other hand, a general numerically controlled machine tool is used to machine a prototype or a model, then it is necessary to accurately define machine coordinates, a machine origin, program coordinates, a machining origin, and other data. While it is not impossible to define those data, the required programming process is too time-consuming and troublesome for machining a portion of a single workpiece.